The evolved packet core (EPC) is the core network of advanced mobile communications systems. The EPC allows different radio access technology (RATs) to operate in an integrated manner. These radio access technologies include first generation wireless local area networks (LANs), second generation (2G) systems, such as global system for mobile communication, or GSM, third generation systems (3G), such as the universal mobile telecommunication system (UMTS), and fourth generation systems (4G) such as long-term evolution (LTE). LTE is a specification promulgated by the 3rd Generation Partnership Project, hereinafter, “3GPP specification”.
Wireless mobile communication technology uses various standards and protocols to transmit data between a node (e.g., a transmission station or a transceiver node) and a wireless device (e.g., a mobile device). Some wireless devices communicate using orthogonal frequency-division multiple access (OFDMA) in a downlink (DL) transmission and single carrier frequency division multiple access (SC-FDMA) in an uplink (UL) transmission. Standards and protocols that use orthogonal frequency division multiplexing (OFDM) for signal transmission include the LTE (3GPP), the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard (e.g., 802.16e, 802.16m), which is commonly known to industry groups as WiMAX (worldwide interoperability for microwave access), and the IEEE 802.11 standard, which is commonly known to industry groups as WiFi.
In 3GPP radio access network (RAN) LTE systems, the node can be a combination of evolved universal terrestrial radio access network (E-UTRAN) NodeBs (also commonly denoted as evolved NodeBs, enhanced NodeBs, eNodeBs, or eNBs), and radio network controllers (RNCs). The eNBs communicate with a wireless device known as an user equipment (UE). The DL transmission can be a communication from the node (e.g., the eNB) to the wireless device (e.g., the UE), and the UL transmission can be a communication from the wireless device to the node.
A UE such as a cellphone can support multiple RATs, known as a multi-mode UE. Only one RAT is operable at a time in the multi-mode UE. A multi-mode UE 50 that is said to be “camped” on one RAT is utilizing only the technology of that RAT. The UE can be switched from one RAT to another, thus switching where the UE is camped. Thus, the multi-mode UE can be camped on LTE, get switched from the 4G RAT to the 3G RAT, and is thereafter camped on UMTS.
Under carrier aggregation, the UE can simultaneously communicate with two different RATs. Thus, the UE is able to concurrently utilize radio resources from multiple carrier frequencies.
In homogeneous networks, the eNB, also called a macro node or macro eNB, can provide basic wireless coverage to wireless devices in a cell. The cell can be the physical region or area inside which the wireless devices are operable to communicate with the macro eNB. Heterogeneous networks (HetNets) can be used to handle the increased traffic loads on the macro nodes due to the increased usage and functionality of wireless devices. HetNets can include a layer of planned high-power macro eNBs overlaid with layers of lower power nodes (small-eNBs, micro-eNBs, pico-eNBs, femto-eNBs, or home eNBs (HeNBs)) that can be deployed in a less well-planned or even entirely uncoordinated manner within the coverage area (cell) of a macro node. The lower power nodes (LPNs) can generally be referred to as “low power nodes”, small nodes, or small cells.
The macro node can be used for basic coverage. The low power nodes can be used to fill coverage holes, to improve capacity in hot zones or at the boundaries between the macro nodes' coverage areas, and to improve indoor coverage where building structures impede signal transmission. Inter-cell interference coordination (ICIC) or enhanced ICIC (eICIC) can be used for resource coordination to reduce interference between the nodes, such as macro nodes and low power nodes, in a HetNet.
HetNets can use time-division duplexing (TDD) or frequency-division duplexing (FDD) for downlink or uplink transmissions. TDD is an application of time-division multiplexing (TDM) to separate downlink and uplink signals. In TDD, DL and UL signals can be carried on the same carrier frequency, where the DL signals use a different time interval from the UL signals. Thus, the DL signals and the UL signals do not generate interference with each other. TDM is a type of digital multiplexing in which two or more bit streams or signals, such as a DL or UL signal, are transferred apparently simultaneously as sub-channels in one communication channel, but are physically transmitted on different time resources. In FDD, a UL transmission and a DL transmission can operate using different frequency carriers. In FDD, interference can be avoided because the DL signals use a different frequency carrier from the UL signals.
Time-division duplexing (TDD) offers flexible deployments without requiring a pair of spectrum resources. Long-term evolution (LTE) TDD allows for asymmetric uplink-downlink (UL-DL) allocations.
As the UE operates in a wireless neighborhood, the channel conditions change. This can be due to movement by the UE, the presence of buildings and vehicles in the line of sight of the UE, and other conditions such as, for example, interference from neighboring stations, etc. Channel state information (CSI) is data about the channel conditions and is provided to the eNB by the UE during wireless communication. CSI includes channel quality information (CQI), pre-coding matrix indication, rank indication, and other characteristic information about the wireless channel.
The 3GPP organization includes several working groups dedicated to particular tasks under LTE. Radio access network 1 (RAN1) is responsible for defining the physical layer; RAN2 deals with radio interface protocols on top of the physical layer; RAN3 pertains to the overall UTRAN (EUTRAN) architecture; RAN4 is dedicated to the RF conformance aspects of UTRAN (EUTRAN), test specifications for radio network and terminal equipment regarding RF transmission and reception performance; and RAN5 pertains to radio interface conformance test specification, test specifications based on RAN4 specifications, and signaling procedures defined by other groups such as RAN2.
Under the LTE specification, the UE monitors a frequency (also known as a layer, frequency layer, carrier, or band) for the serving primary cell (pcell) of the UE as well as for a secondary cell (scell) of the UE. While being serviced by the pcell, the UE remains on the pcell frequency. The pcell frequency layer and the scell frequency layer are monitored at a first rate.
Additionally, the UE monitors other frequencies, including other RATs, at a second, lower rate, such that, if handover to a different frequency band (in the case of inter-RAT monitoring) or switching to a different RAT, such as USTM (3G) or WiFi (2G) becomes necessary, the UE knows the characteristics of these frequency layers.
Previously under LTE, the UE was expected to monitor eight or more frequency layers. Under recent RAN4 modifications (RAN4, release 12), the minimum number of frequency layers in EUTRAN to be monitored has increased from eight to thirteen.
Thus, there is a need for a cell identification and measurement method that addresses the RAN4 release 12 requirements.